What I mean is that I could design a site i.e. bitex.ro , take your payments ,
and have a simple math formula deduct % as a profit for me and
have the rest divided as a (weekly, daily, monthly take your pick) payments to you.
Taking account of difficulty exchange rates etc.etc.
Zero investments pure profit.
How would you know that you're actually not mining anything?
The provider should post information about the blocks they discover
here is an example of Cex.io:
https://blockchain.info/block-index/000000000000000a6b380a29e3570fc08f4d9001fc203c4355beab1f9037c02b
you may give it a try: